Ordnance powder bag



ORDNANCE POWDER BAG Filed Aug. 7, 1941 IN V EN TOR.

W; Ram Mydahfi Patented July 30, 1946 UNl TED STATES PATENT OFFICE 1 Claim.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to ordnance powder bags or containers.

In large caliber guns it is customary to load a projectile into a gun through an opened breach, then to insert propellent powder in an amount to give the desired range. Finally, the detonator is inserted and the breach closed. The propellent powder, which is usually a pyrocellulose or mixed pyrocellulose-nitroglycerine composition formed into grains varying in size with the gun caliber and containing perforations to control the rate or" burning, is contained in a sack or bag. One important and necessary characteristic of the material from which these bags is made is that following the explosion, whatever residue remains must cease immediately to burn, glow, or smoulder and so make possible the immediate introduction of the next charge with safety. This property is lacking in all fibers of vegetable origin.

For many years, powder bags for large caliber ordnance have been made from a natural silk cloth. Silk has the desired property of no after glow but is expensive-and is obtainable only from foreign sources.

An object of this invention is to devise ordnance powder bags or containers made chiefly from other than naturally occurring animal or vegetable fibers.

Another object is to devise such powderbags from materials which, in addition to the attributes of silk, possess the advantages of being inexpensive, readily available, and highly stable during long periods of storage.

In accordance with my invention, it is desirable to construct ordnance powder bags from synthetic organic materials which have the following desirable properties:

1. These materials should burn or be consumed during the explosion of thepropellent powder and if any residue remains at the termination of such explosion, said residue should immediately cease to burn, glow or smoulder.

2. These materials should burn with the least possible residue, thus minimizing gun fouling; and further, any residue which remains should neither contain nor generate substances corrosive to the gun barrel.

3. The materials should be readily available from domestic sources and be low in cost.

4. The materials should be stable when subjected to moisture, light, and storage even when in contact with pyrocellulose and other mixed propellents.

5. The containers or bags should have mechanical strengthadequate to retain the powder and to permitthe reasonably rough handling that may be required under the pressure of battle.

6. The powder bag material should introduce no new defects or hazards such as the holding of static electric charges or the release of acrid or toxic vapors which might affect men within a gun turret housing.

In addition to the foregoing properties, these materials should also possess the following advantages which, however, are not prerequisites for a satisfactory and acceptable powder bag.

7. The materials should have properties which are well-known. These materials should be able to be readily worked or prepared on equipment which has already been developed and is readily available.

8. The materials should be light in weight and so add little to transport difliculties. They should be low in bulk and so require no changes in the volume or design of the present gun barrels.

9. The containers made from these materials should be waterproof and watertight, thus permitting the use of component parts of the propellent charge which are sensitive to water.

The above and other features of my invention may be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawing wherein the single figure represents a cross-section through a powder bag incorporating my invention.

I may construct my novel powder bags of a. ntirocellulose composition. Such a material possesses in great measure all of the advantages outlined above. Since the major component of the propellent charge is nitrocellulose (usually pyrocellulose of between 12 and 13.4% nitrogen) a nitrocellulose bag introduces a material not dissimilar to the propellent charge. However, for the powder bags, I prefer to use a nitrocellulose of somewhat lower nitrogen content than pyrocellulose, such as a plastic or coating grade of nitrocellulose, i. e., of about 10 to 12% nitrogen.

The nitrocellulose may be employed in the formation of powder bags in a number of ways. For example, nitrocellulose may'first be dissolved in suitable solvents. 'Such solvents, which may be employed singly or in various combinations, include the following types: Alcohols, aldehydes, ketones, chlorinated hydrocarbons, ethers, esters, nltroparaflins, hydroxyaldehycles, hydroxykeesters, lactic acid esters, and the like.

tones, and the like. Aliphatic, aromatic and alicyclic hydrocarbons may be employed as diluen s. The specific solvents or combination of solvents chosen will depend on a number of factors which include the boiling or evaporation ranges desired, the degree if nitration of the nitrocellulose employed, the viscosity characteristics desired in the solution to be cast or coated, the solubility characteristics of the plasticizers, resinous materials, cellulose ethers, and the like, which may be incorporated, the flammability of the solvent mixture, the ease of solvent recovery, resistance to film blushing, etc.

The nitrocellulose solution thus prepared may be cast in the form of a film or may be used to coat a fabric backer as will be described below. As already stated plasticizers and resinous bodies may be incorporated in the solution before the film is castso as to impart to the film the desired degree of flexibility and strength.

Among the plasticizers that may be used, singly or in various combinations to give plasticity or suppleness to the film are the following types; camphor, triaryl and trialkyl phosphates, phthalate esters, aryl and alkyl sulfonamides, butylphthalyl-butyl-glycollate and related materials, castor oil, blown and heat-bodies vegetable oils, methyl abietate, tartaric acid esters, citric acid Where a minimum of ash and corrosive products are desired, it is preferable to avoid the use of plasticizers containing inorganic constituents, such as tricresyl phosphate and chlorinated diphenyls.

Among the resinous materials that may be employed, singly or in various combinations to add body, stiffness, stability, or other modifying property to the film are: Alkyd resins, preferably in the B or soluble stage, rosin, rosin esters, toluene sulfonamide-formaldehyde resins, furfuralketone resins, dammar, terpene resins, ureaformaldehyde resin solutions in butanol, melamine-formaldehyde resins, and the like.

The nitrocellulose which is dissolved as described above is preferably selected from materials having a nitrogen content range of to 12%. The viscosity properties may likewise be selected to secure a coating or casting solution of the desired properties. Where proper consideration is given to the plasticizers Or other materials present in the solution, scrap nitrocelullose film or other waste nitrocellulose products may be employed.

The film may be formed in any suitable manher, as by casting and drying in th usual way.

The film is then formed into bags or sacks by stitching, as with silk thread, or by cementing with resinous or nitrocellulose composition adhesives or with medium-boiling nitrocellulose solvents such as the monoethyl ether of diethylene glycol.

Instead of constructing the powder bag of a single thicknessof film as described above, the bag maybe made of laminated material as shown in the drawing. The inter-layer I may b of some light weight fabric such as silk mummy cloth, which is a silk cheesecloth having a very low weight of silk per square yard. Likewise this interlayer may be of wool, cellulose acetate, synthetic casein or soy bean fiber cloth, nitrocellulose fabric which may be prepared as described below, and such other synthetic fabrics as represented by -nylon. On each side of the interlayer l is formed the films 2 and 3 cast, coated or cemented on said interlayer. Where the edges of the laminated material forms a seam as, for example, is

tein-p-lastic film in order to secur lower inflammability in handling and transportation, reduced tendency toward accumulation of static electric charges or other modified physical properties. Since the physical properties thus enumerated are usually desirable for the external surface of the bag, preferably such material will b substituted for the nitrocellulose layer 2 as shown in the drawing.

One method of producing the laminated struc- V ture as shown in the drawing is to pass the light weight textile materials enumerated above in a continuous web under a spray of or through the nitrocellulose plasticized lacquer solutions to produce thereon a continuous film. In order to secure sufficient thickness multiple coats may be required with drying of the film with each application.

If desired the final coating may be of some other film forming material such as ethyl cellulose, cellulose acetate, isobutene polymer, casein, zein, etc., in order to secure modification of the physical properties, especially as it relates to flammability during handling and transportation and reduced tendency toward th accumulation of static electrical charges.

The use of low viscosity nitrocellulose in the above process will permit the building up of coatings of appreciable thickness with a minimum number of applications. Comparatively thick sheets of nitrocellulose films may be applied to the fabric web from aqueous emulsions by dipping or under a doctor knife with the advantages of reduced solvents, elimination of solvent recovery systems, lowered fire hazard and ease of application.

Nitrocellulose film, especially in the thicker gauges, may be deep-drawn by the application of heat and pressure to make seamless containers of high mechanical strength and water resistance with low weight and bulk. Such a container, e. g., a cylinderwith bottom integrally formed and having a diameter to fit snugly into the gun barrel can be filled with the powder charge and the top sealed by crimp-fitting or cementing in plac a circular disc of the same material. Such a method of processing lends itself readily to mass production technique.

Instead of making the powder bags of nitrocellulose film, the powder bags may be made in fabric form from spun nitrocellulose yarn that has not been denitrified, i. e., treated to hydrolyze .ofi some of the nitrate groups and thus reduce its infiammability. Such nitrocellulose fabrics can easily be made by nitrating purified cotton fabric of the correct weight and weave in batch nitrations or even in continuous process nitration. Conventional nitrating mixtures of nitric and sulfuric acids are used with carefully controlled temperatures. Thereafter the nitrated' fabric is washed, stabilized by boiling in dilute acid'solutions, then in water, then in dilute alkaline solutions, and then again in water to remove hemicelluloses, cellulose sulfates and low nitrate esters that contribute to instability. Th material is then dried. Y

In batch nitrations the foregoing process could be carried out either on the piece goods or on the complete cotton bags after cutting and sewing. Under carefully controlled conditions of nitration, the cotton fabric not only does not lose its mechanical strength but such strength may be increased. In this form, nitrocellulose of any degree of nitration between 9% and 14% nitrogen may be employed although I prefer to use a collo dion stage with nitrogen content of about 10% to 12%.

Were the powder bags to -be made of nitrocellulose yarn, it is desirable to nitrate the cotton cloth or the completed bags as described above in order to eliminate the necessity of looming so inflammable material as nitrocellulose yarn.

In the arrangement as shown in the drawing the interlayer i may be made of a light weight cotton cloth nitrated as described above. Such 'nitrated cloth as 'I have described above 'may be" modified by immersion in solvents, in solventplasticizer mixtures, in solvent-plasticizer-resin solutions, all with or without the addition of non-solvent diluents, e. g., hydrocarbons. By such treatment over controlled periods of time, partial or extensive swelling or colloidizing of the nitrated fiber may be accomplished, together with absorption by the fiber of such plasticizers and/or resins that have solvent power or affinity for nitrocellulose. Dyes, which, for example may be used to characterize the type of powder to be contained in the bag, may be incorporated at this stage. On subsequent drying, such treatment will serve to cement adjoining fibers together to give a more impervious and stiffer fabric, though the latter may be modified Widely by the choice of plasticizers and/or resins that may be employed. The solvents, plasticizers and resins already listed above are suitable for this purpose.

The nitrocellulose of which my novel powder bags are made may be employed mixed with cellulose ethers such as ethyl cellulose in order to control its various physical properties such as rate of burning, stiffness, melting or softening point.

The finished nitrocellulose bag or container may be given a coating of graphite in a thin lacquer or other suitable adhesive or binder in order to facilitate the ready dissipation of any static electrical charges that may accumulate. The same end may be achieved by coating the bags with very thin films of hygroscopic or moisture-retaining material such as gelatin-glycerolwater combinations, with or without the incorporation of graphite.

Nylon, which I have mentioned above, is formed by the condensation of aliphatic dicarboxylic acids with aliphatic diamines. It is a molecularly oriented, high-molecular weight polyamid and as such bears a close chemical relationship to silk and wool. It melts at a lower temperature than does silk, but fails to burn when exposed to a free flame, even when a thin fabric of this material is held directly in a flame. This material, drawn into filaments suitable for knitting or spinning, can be formed into powder bags or sacks that will show no after-glow following the combustion of the explosive charge. Alternatively, the material can be extruded through a slit and stretched before cooling to yield a strong, durable, light-weight film that may be formed into powder containers by stitching or cementing. As already stated, thin nylon fabrics may serve as the interlayer I of the laminated material as shown in the drawing.

Ethyl cellulose, which I have indicated may be used as a component part of my novel powder bag, has properties which are desirable in this respect. Tests on commercial ethyl cellulose and cast ethyl cellulose film have shown the material to have a very low degree of flammability, and films once lighted have no tendency to continue to burn, glow or smoulder when the igniting flame is removed. Ethyl cellulose film may be made in a variety of film-thicknesses, widths and in combination with a variety of plasticizers, resins and waxes to give films having a wide variety of physical characteristics. In addition to using ethyl cellulose in a laminated material, the ethyl cellulose film itself may be utilized. Powder bags can be formed from such film by stitching or cementing. Ethyl cellulose iscompatible with nitrocellulose and may be used in combination with nitrocellulose, together with plasticizers and resins if desired, to give films having modified physical properties, such as the rate of burning, decreased flammability during handling and transportation, and increased flexibility.

Other cellulose ethers, such as benzyl cellulose, have similar properties and may be substituted for ethyl cellulose in these applications.

Ethyl cellulose is soluble in a wide variety of solvents, particularly in mixed solvents, and is compatible with a wide variety of plasticizers, resins, waxes, raw, blown or heat-bodied oils, bituminoussubstances, etc., making possible the formation of film having a wide variety of physical properties.

Cellulose acetate, mentioned as a component part of the laminated material from which my novel powder bags may be made, also has properties suitable for this purpose. Flame tests on commercial cellulose acetate film have shown that the material burns and also fuses readily, but the films once lighted have no tendency to continue to burn, glow or smoulder when the igniting fiame is removed. Cellulose acetate is available in the form of yarn and in a great variety of woven and knitted fabrics, and also in the form of film in a variety of widths, thicknesses and plasticizer-resin compositions having a wide variety of physical properties. In addition to the use of cellulose acetate as one or more of the layers of the laminated structure as shown inthe drawing, powder bags may be made by knitting cellulose acetate yarn or by cutting and stitching suitable cellulose acetate fabrics into the desired shapes. The finished fabric container may be coated with films of nitro-cellulose to accelerate burning during the combustion of the charge or to make the container more impervious to moisture transfer.

The cellulose acetate film, especially in the thicker gauges, may be deep-drawn by the application of heat and pressure to form seamless containers of high mechanical strength. Such a container, e. g., a cylinder with an integrally formed bottom and having a diameter snugly fitting the gun barrel can be filled with the powder charge and the top sealed by crimp-fitting or cementing in place a circular disc of the same material. Such a processing method lends itself readily to mass production technique.

Similarly, as detailed above in the application of nitrocellulose and ethyl cellulose to this problem, cellulose acetate film can be formed into bags by stitching or cementing, or composite film of high mechanical strength can be produced by laminating two cellulose acetate films to a reinforcing interlayer of suitable fabric. Or, for one of the cellulose acetate films in the composite film, other film materials may be substituted,

e.; g., nitrocellulose film to give accelerated burning during the combustion of the charge.

, Fabrics may be coated with cellulose acetate compositions (cellulose acetate, together with ready described, isobutene polymers may be used 7 in the construction of powder bags.

Isobutene polymers are available in different degrees of polymerization ranging from thick syrup-like fiuids to rubber-like materials. These materials have the unique property of volatilizing without residue when subjected to temperatures of 400-500 F. and higher. These isobutene polymers are compatible in general with ma terials having very low contained oxygen percentages, e. g., Waxes in general, including paraffin and ozokerite waxes, petrolatum, rubber, asphalts, pitches, rosin, rosin esters, dammar, terpene resins, and the like. Isobutene polymers can be compounded with various combinations of the above substances and dissolved in aliphatic, aromatic or alicyclic hydrocarbons, terpenes, chlorinated hydrocarbons, etc. to yield a material suitable for coating fabrics such as those listed above as reinforcing-interlayers, to yield suitable bag or container material or for coating other sheet or film material to secure modification of the physical properties of the latter. Isobutene polymers, suitable for use according to the invention, appear on the market under the trade name Vistanex.

The protein-plastic materials mentioned above as being useful in film form as one of the layers of the laminated structure shown in the drawing are also available in fabrics and in woven and knitted fabrics. Such protein-plastic materials have been made from purified casein and soy proteins and also from zein from corn. The chemical nature of these materials bear a close relationship to that of silk and wool and such materials may be made into powder bags or contain ers that meet the basic requirements of a satisfactory powder bag. These materials may be compounded with suitable plasticizers, resinous materials, waxes, etc., and cast into films, coated on fabrics or upon other film material to yield desirable products for my purpose. The resulting films may be hardened or cured by treatment with formaldehyde and may be rendered less sensitive to water and more readily inflammable during combustion of the charge by a coating of cellulose-nitrate, wax, resin, or similar materials,

It is desirable to avoid the use of fixed alkalis and the like as solubilizers in preparing the protein solutions, or the use of alums, chromic salts and the like as hardening or curing agents, as such a practice will lead to a high ash or residue in the gun after combustion. Urea and various aliphatic amines make suitable protein solubilizing agents, though zein is readily dissolved in ethanol. Polyhydric alcohols and amides make suitable plasticizers and rosin, manilla copal, and shellac are examples of suitable resins for use in such compositions to add to the body and modify the film properties. These protein film materials have no tendency toward the accumulation of static electric charges.

The term coating as used in the appended claim is intended to include applied pre-formed films as well as coverings applied in liquid or plastic form. i

What is claimed is:

An ordnance powder bag of the type which when filled with a propellent powder charge is adapted for insertion into a gun barrel for use as the propellant for separate loading ammunition, said bag having its walls formed of a composite sheet-like material formed of a light weight combustible fabric on each side of which is a film of nitrocellulose adhering thereto and having upon the nitrocellulose film exteriorly of the bag a coating of a combustible material which has less flammability and less tendency to accumulate static electricity than nitrocellulose, and having upon the last mentioned coating a coating comprising a material which is a conductor of electricity whereby static electric charges accumulatin 'upon the bag may be allowed to escape from the bag.

WILLIAM E. MYDANS. 

